Reflection Refraction Notes

1
Reflection / RefractionNotes
2
Reflection and Refraction

• When a light ray travels from one medium to
  another, part of the incident light is reflected
  and part of the light is transmitted at the
  boundary between the two media.
• The transmitted part is said to be refracted in
  the second medium.

incident ray
reflected ray
refracted ray
3
Types of Reflection

• If the surface off which the light is reflected
  is smooth, then the light undergoes specular
  reflection (parallel rays will all be reflected
  in the same directions).
• If, on the other hand, the surface is rough, then
  the light will undergo diffuse reflection
  (parallel rays will be reflected in a variety of
  directions)

4
The Law of Reflection

• For specular reflection the incident angle qi
  equals the reflected angle qr
• qi qr

The angles are measured relative to the normal,
shown here as a dotted line.
5
Forming Images with a Plane Mirror

• A mirror is an object that reflects light. A
  plane mirror is simply a flat mirror.
• Consider an object placed at point P in front of
  a plane mirror. An image will be formed at point
  P behind the mirror.

do distance from object to mirror di distance
from image to mirror ho height of object hi
height of image
hi
ho
do
di
For a plane mirror do -di and ho hi
6
Images

• An image is formed at the point where the rays of
  light leaving a single point on an object either
  actually intersect or where they appear to
  originate from.
• If the light rays actually do intersect, then the
  image is a real image. If the light only appears
  to be coming from a point, but is not physically
  there, then the image is a virtual image.
• We define the magnification, m, of an image to be

7
Plane Mirrors
Image
Object
8
Plane Mirrors

• A plane mirror image has the following
  properties
• The image distance equals the object distance (
  in magnitude )
• The image is unmagnified
• The image is virtual
• negative image distance
• di lt 0

do
di
9
The Refraction of Light

• The speed of light is different in different
  materials. We define the index of refraction, n,
  of a material to be the ratio of the speed of
  light in vacuum to the speed of light in the
  material
• n c/v
• When light travels from one medium to another its
  velocity and wavelength change, but its frequency
  remains constant.

10
Index of Refraction
n c / v ³ 1
11
Snells Law
In general, when light enters a new material its
direction will change. The angle of refraction q2
is related to the angle of incidence q1 by
Snells Law where v is the velocity of light in
the medium. Snells Law can also be written
as n1sinq1 n2sinq2
Normal line
The angles q1 and q2 are measured relative to the
line normal to the surface between the two
materials.
12
Total Internal Reflection

• When light travels from a medium with n1 gt n2,
  there is an angle, called the critical angle qc,
  at which all the light is reflected and none is
  transmitted. This process is known as total
  internal reflection. The critical angle occurs
  when q2 90 degrees

Total internal reflection if sinq2gt1
The incident ray is both reflected and refracted.
Total Internal Reflection
13
Dispersion

• In a material, the velocity of light (and
  therefore the index of refraction) can depend on
  the wavelength. This is known as dispersion.
  Blue light travels slower in glass and water than
  does red light.

As a result of dispersion, different colors
entering a material will be refracted into
different angles. Dispersive materials can be
used to separate a light beam into its spectrum
(the colors that make up the light beam).
Example prism
14
Dispersion in a Prism
15
The Rainbow
No two people ever see the same rainbow
16
(No Transcript)
17
(No Transcript)
18
Mirage
Cool air
Warm air
Surface of water?
19
(No Transcript)
20
(No Transcript)
21
Looming
Warm air
Cool air
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
Green Flash
Earth
Sun
Dispersion occurs causing multiple images of the
sun. The last to set would be blue, but most of
the blue has been scattered which leaves green.
27
Green Flash
28
http//virtual.finland.fi/stream/The_Green_Flash_o
n_video.ram